1. Field of the Invention
The present invention relates to a flow rate measuring apparatus that is installed, for example, by insertion into an insertion hole formed in an intake pipe for measuring the flow rate of air that passes through a piping passage in the intake pipe.
2. Description of the Related Art
In FIGS. 1 and 2 of a first patent document (Japanese patent application laid-open No. H11-14423), there is shown a flow rate measuring apparatus that has a housing portion 3 containing therein a circuit board 6 on a metal base 5, and an auxiliary passage member 4 formed separately from each other. This housing 3 made of resin includes a frame portion 31, a connector portion 32 that has a connector terminal 33 embedded therein, a stationary portion 34 that fixedly secures a plurality of support terminals 35 supporting a heat generation resistor 1 and a thermally sensitive resistor 2, and a fixed flange 36.
The metal base 5 covers an opening face at one side of a cavity in the housing 3 together with an opening face of an auxiliary air passage at which one side of the auxiliary passage member 4 is opened, and at the same time, it is fixedly attached to the frame portion 31 and the auxiliary passage member 4.
The heat generation resistor 1 and the thermally sensitive resistor 2 arranged in the auxiliary passage member 4 is spaced from the metal base 5, and is electrically connected to the circuit board 6 through the support terminals 35.
In addition, another flow rate measuring apparatus is shown in FIG. 3 of a second patent document (Japanese patent application laid-open No. 2001-124606). A module housing 4 is arranged on a metal base 5, and a heat generation resistor 7, a temperature sensitive resistor 8 and an intake air temperature sensor 9 are fixedly secured by spot welding to and electrically connected to a support terminal 2 that is integrally molded with the module housing 4.
In this flow rate measuring apparatus, the heat generation resistor 7, the temperature sensitive resistor 8 and the intake air temperature sensor 9 are disposed in the auxiliary air passage 12 that is formed by the metal base 5 and bypass molding 10.
The flow rate measuring apparatus described in the above-mentioned first patent document is influenced by the heat of a flow meter body 86 itself other than a thermal influence due to the own heat of electronic circuit parts.
The influence of the heat of the flow meter body 86 is that when the temperature of air flowing through the hollow interior of the flow meter body 86 becomes low while the temperature of the flow meter body 86 is high, the heat of the flow meter body 86 is transmitted to the heat generation resistor 1 and the thermally sensitive resistor 2, whereby a detection error becomes large due to the influence of the heat thus transmitted.
In case of an intake pipe of an automotive internal combustion engine, the intake air in the interior of the intake pipe is in a cold state when the temperature of the outside air is low, but the intake pipe itself might become a warm state by receiving a thermal influence of the internal combustion engine.
In case where such a kind of flow rate measuring apparatus is applied to a fuel injection system of such an automotive internal combustion engine, there arises the following problem. That is, the heat of the intake pipe is transmitted to the heat generation resistor 1 and the thermally sensitive resistor 2 through the metal base 5 and the support terminal 35, thus resulting in a cause of a flow rate detection error.
Moreover, similarly, in the flow rate measuring apparatus described in the above-mentioned second patent document, too, there has been the following problem. That is, the heat of the intake pipe or the heat due to own heat generation of the circuit board 6 in the module housing 4 installed in the intake pipe is transmitted to the heat generation resistor 7 and the temperature sensitive resistor 8 through the metal base 5 and the support terminal 2, thus resulting in a cause of a flow rate detection error.
Further, the flow rate measuring apparatus described in the above-mentioned first patent document is fixedly secured to the flow meter body 86, which forms the main air passage 81, by means of the fixed flange 36 of the housing 3 through the metal base 5, but the flow rate measuring apparatus at this time is of a cantilever structure in which the fixed flange 36 is fixedly supported at its base end portion with its tip end portion being free.
Thus, there has also been the following problem. That is, when the flow meter body 86 is caused to vibrate, a concentrated stress is generated in the vicinity of the fixed flange 36 among fixedly secured portions between the metal base 5 and the housing 3, so in the fixed portions at this location, the metal base 5 might be peeled off from the housing 3, or an electrically conductive lead 7 electrically connecting the circuit board 6 and the support terminals 35 to each other might be broken or disconnected.